Installation

If you see an error such as "Call to 'node findJavaHome.js' returned exit status 1"
Try running node findJavaHome.js in the node-java directory to see the full failure message.

If you are having problems finding 'jni.h'. Make sure you have the JDK installed not just the JRE. If you are using
OpenJDK you want the openjdk-7-jdk package, not openjdk-7-jre. Mavericks users see Issue #86 if you run into this.

Installation OSX

If you run into strange runtime issues, it could be because the Oracle JDK does not advertise itself as available for JNI. See Issue 90 for more details and manual workarounds. If this does occur for you, please update the issue.

Installation Windows

For 64 bit installs with 32 bit node:

you need the 32 bit JDK, with the 64 bit JDK you will see LNK2001 errormessages (http://stackoverflow.com/questions/10309304/what-library-to-link-to-on-windows-7-for-jni-createjavavm).

when using the windows SDK 7.1 command prompt (64 bits) be sure to setenv.cmd /Release /x86

If you get ENOENT errors looking for <nodepath>\node_modules\node-gyp\.., ensure you have node-gyp installed as a global nodule:

npm install -g node-gyp

If you get D9025 warnings and C1083 errors when looking for .sln or .h files, be sure you've got the node-gyp's dependencies, as explained here.

Java 1.8 support

Manual compilation for Java 1.8 support requires additional steps:

./compile-java-code.sh

./compile-java8-code.sh

node-gyp configure build

npm test

Java 1.8 language features can be used in Java classes only if a Java 1.8 JRE is available. The script compile-java8-code.sh is used only to compile java classes used in the 'test8' unit tests, but these classes are checked into the test8/ directory. Note that unit tests in the test8/ directory will pass (by design) if run against a Java 1.7 JRE, provided that a java.lang.UnsupportedClassVersionError is caught with the message 'Unsupported major.minor version 52.0' (the expected behavior when Java 1.8 language features are used in an older JRE).

Installation node-webkit

npm install -g nw-gyp

npm install java

cd node_modules/java

nw-gyp configure --target=0.10.5

nw-gyp build

See testIntegration/webkit for a working example

Using node-java in existing maven projects

When using node-java in existing maven projects, all the dependencies and the class files of the project have to be pushed to the classpath.

One possible solution would be:

Issue the command:

mvn dependency:copy-dependencies

Then create the following module javaInit:

"use strict";

var fs =require("fs");

var java =require("java");

var baseDir ="./target/dependency";

var dependencies =fs.readdirSync(baseDir);

dependencies.forEach(function(dependency){

java.classpath.push(baseDir +"/"+ dependency);

})

java.classpath.push("./target/classes");

java.classpath.push("./target/test-classes");

exports.getJavaInstance=function(){

return java;

}

and then in the consuming class write:

var javaInit =require('./javaInit');

var java =javaInit.getJavaInstance();

//your code goes here

Quick Examples

var java =require("java");

java.classpath.push("commons-lang3-3.1.jar");

java.classpath.push("commons-io.jar");

var list1 =java.newInstanceSync("java.util.ArrayList");

console.log(list1.sizeSync());// 0

list1.addSync('item1');

console.log(list1.sizeSync());// 1

java.newInstance("java.util.ArrayList",function(err,list2){

list2.addSync("item1");

list2.addSync("item2");

console.log(list2.toStringSync());// [item1, item2]

});

var ArrayList =java.import('java.util.ArrayList');

var list3 =newArrayList();

list3.addSync('item1');

list3.equalsSync(list1);// true

Create a char array

var charArray =java.newArray("char","hello world\n".split(''));

Create a byte array

Using java.lang.Long and long

JavaScript only supports 32-bit integers. Because of this java longs must be treated specially.
When getting a long result the value may be truncated. If you need the original value there is
a property off of the result called "longValue" which contains the un-truncated value as a string.
If you are calling a method that takes a long you must create it using java.newInstance.

Exceptions

Exceptions from calling methods either caught using JavaScript try/catch block or passed
to a callback as the first parameter may have a property named "cause" which has a reference
to the Java Exception object which caused the error.

try{

java.methodThatThrowsExceptionSync();

}catch(ex){

console.log(ex.cause.getMessageSync());

}

AsyncOptions: control over the generation of sync, async & promise method variants.

As of release 0.4.5 it became possible to create async methods that return promises by setting the asyncOptions property of the java object. With release 0.4.7 this feature is extended to allow changing the suffix assigned for sync and async method variants, and to further configure this module to optionally omit generation of any of these variants.

NOTES:

If you want the defacto standard behavior, simply don't set java.asyncOptions.

If you do provide asyncOptions, be aware that this module will not generate method variants of a given flavor if you don't provide a string value for the corresponding suffix (asyncSuffix, syncSuffix, promiseSuffix). In the example above, the application is configured to omit the method variants using node-style async callback functions.

If you provide asyncOptions.promiseSuffix then you must also set asyncOptions.promisify to a function that promisifies a node-style async function. I.e. the provided function must take as input a function whose last argument is a node callback function, and it must return an equivalent promise-returning function. Several Promises/A+ libraries provide such functions, but it may be necessary to provide a wrapper function. See testHelpers.js for an example.

If you provide asyncOptions.promisify then you must provide a non-empty string for asyncOptions.promiseSuffix.

Either (but not both) asyncSuffix or syncSuffix can be the empty string. If you want the defacto standard behavior for no suffix on async methods, you must provide an empty string for asyncSuffix.

We've tested promises with five Promises/A+ implementations. See testHelpers.js for more information.

NOTE: Due to specifics of initialization order, the methods java.newInstancePromise, java.callMethodPromise, and java.callStaticMethodPromise are not available until the JVM has been created. You may need to call some other java method such as java.import() to finalize java initialization, or even better, the function java.ensureJvm().

Special note about the exported module functions newInstance, callMethod, and callStaticMethod.

These methods come in both async and sync variants. If you provide the promisify and promiseSuffix attributes in asyncOptions then you'll also get the Promises/A+ variant for these three functions. However, if you change the defacto
conventions for the syncSuffix (i.e. 'Sync') and/or asyncSuffix (i.e. '') it will not affect the naming for these three functions. I.e. no matter what you specify in asyncOptions, the async variants are named newInstance, callMethod, and callStaticMethod, and the sync variants are named newInstanceSync, callMethodSync, and callStaticMethodSync.

Varargs support

With v0.5.0 node-java now supports methods with variadic arguments (varargs). Prior to v0.5.0,
a javascript call to a Java varargs method had to construct an array of the variadic arguments using java.newArray(). With v0.5.0 javascript applications can simply use the variadic style.

In most cases it is still acceptable to use java.newArray(). But it is now possible to pass a plain javascript array, or use the variadic style. For example, consider these snippets from the unit test file test/varargs-test.js:

Note that when passing a Javascript array (e.g. ['a', 'b', 'c']) for a varargs parameter, node-java must infer the Java type of the array. If all of the elements are of the same javascript primitive type (string in this example) then node-java will create a Java array of the corresponding type (e.g. java.lang.String). The Java types that node-java can infer are: java.lang.String, java.lang.Boolean, java.lang.Integer, java.lang.Long, and java.lang.Double. If an array has a mix of Integer, Long, and Double, then the inferred type will be java.lang.Number. Any other mix will result in an inferred type of java.lang.Object.

Methods accepting varargs of a generic type are also problematic. You will need to fall back to using java.newArray(). See Issue #285.

JVM Creation

With v0.5.1 a new API is available to make it easier for a complex application to have full control over JVM creation. In particular, it is now easier to compose an application from several modules, each of which must add to the Java classpath and possibly do other operations just before or just after the JVM has been created. See the methods ensureJvm and registerClient. See also several of the tests in the testAsyncOptions directory.

Release Notes

v0.5.0

Support for varargs. This change is not 100% backwards compatible, but the fix is generally easy and results in more natural code.

Object lifetime

When you call a Java method through node-java, any arguments (V8/JavaScript objects) will be converted to Java objects on the v8 main thread via a call to v8ToJava (found in utils.cpp). The JavaScript object is not held on to and can be garbage collected by v8. If this is an async call, the reference count on the Java objects will be incremented. The Java method will be invoked in a node.js async thread (see uv_queue_work). When the method returns, the resulting object will be returned to the main v8 thread and converted to JavaScript objects via a call to javaToV8 and the Java object's reference count will then be decremented to allow for garbage collection. The resulting v8 object will then be returned to the callers callback function.

Static member name conficts ('name', 'arguments', 'caller')

The Javscript object returned by java.import(classname) is a Javascript constructor Function, implemented such that you can create instances of the Java class. For example:

var Test =java.import('Test');

var test =newTest();

Test.someStaticMethod(function(err,result){...});

var value1 =Test.NestedEnum.Value1;

But Javascript reserves a few property names of Function objects: name, arguments, and caller. If your class has public static members (either methods or fields) with these names, node-java is unable to create the necessary property to implement the class's API. For example, suppose your class Test implements a static method named caller, or has a NestedEnum with a value name:

publicclassTest{

...

publicstaticStringcaller(){return"something";}

publicenumNestedEnum{ foo, name };

}

In Javascript, you would expect to be able to use those static members like this:

var Test =java.import('Test');

Test.caller(function(err,result){...});// ERROR

var value =Test.NestedEnum.name;// ERROR

Node-java can't create those properties, so the above code won't work. Instead, node-java appends a suffix to the name. The default suffix is simpy an underscore _, but you can change the suffix using asyncOptions:

var java =require('java');

java.asyncOptions={

asyncSuffix:"",

syncSuffix:"Sync",

ifReadOnlySuffix:"_alt"

};

var Test =java.import('Test');

Test.caller_alt(function(err,result){...});// OK

var value =Test.NestedEnum.name_alt;// OK

Troubleshooting

Error: Cannot find module '../build/jvm_dll_path.json'

Either postInstall.js didn't run or there was a problem detecting java. Try running postInstall.js manually.

Debugging

License

(The MIT License)

Copyright (c) 2012 Near Infinity Corporation

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.